1. Technical Field
The present invention relates in general to improvements in communication in a distributed data processing system and in particular to methods and systems for enhancing the efficiency of modem operation in a data processing system. Still more particularly, the present invention relates to methods and systems for permitting command processing by a modem during data transfer, wherein communication channel parameters may be monitored.
2. Description of the Related Art
Data communication between modem computer devices is typically accomplished utilizing a modulator/demodulator or so-called "modem" which is utilized to convert digital signals within a data processing system to analog signals for transmittal over existing communication links. Additionally, such devices convert received analog signals to digital signals for utilization by a data processing system. In the past most distributed computer networks have been coupled together utilizing existing telephone land line systems or specialized wiring; however, modern distributed data processing systems often utilize more sophisticated means of communication.
For example, the decreasing cost of cellular communication equipment has resulted in the utilization of that technology to couple together computers without the necessity of access to a telephone line outlet. This particular technology is particularly effective in combination with small portable battery powered laptop or notebook computers in which the necessary modem and cellular communication circuitry are miniaturized and provided in an integral fashion within the computer itself. Thus, an operator utilizing such a computer may initiate communications and transfer data between his or her computer and a distributed data processing system without the necessity of access to either telephone lines or power lines. Examples of such portable computers include the International Business Machines Corporation LX40 and the Model 9075 PCradio, which may be utilized for wireless communication by attaching a radio device. Radio devices such as a cellular telephone, or ARDIS radio devices may be utilized.
These radio devices communicate with the portable computer via a conventional communication port. These devices are typically configured and controlled in the same manner as a Hayes compatible modem. For example, a series of preselected commands, typically known as "AT" commands may be utilized to set internal parameters for these devices and instruct the devices in operation. Known modems or combination modem/radio systems typically operate in one of two different modes of operation. In a first mode of operation, the device recognizes all characters transmitted to the device as commands. This mode of operation is referred to as the command mode. The other mode treats characters received at the device as data to be transmitted via a communications link. This mode of operation is referred to as the data mode. Typically, a special sequence of data bytes may be utilized to toggle the device from the data mode to the command mode. Generally this sequence consists of one second with no data followed by the key sequence "+++," followed by another second of no data.
This manner of transferring back and forth between command and data modes of operation has proven to be quite adequate for devices which communicate via telephone landlines. Such devices have been widely accepted within the industry. This toggling concept works largely because the command mode and data mode are substantially divorced from one another, without the need to share data from one mode with the second mode. This is generally due to the low bit error rates present within landline systems and the fact that a standard modem has little information to provide to the data processing system regarding modem or line operation while the modem is operating in a data mode. In contrast, modem/radio systems possess substantial amounts of information regarding the modem and communications channel operation.
For example, when utilizing a cellular telephone/modem to transmit data it would be helpful to the operator to possess information regarding how well the cellular telephone radio link is operating at a particular moment. This information may be utilized by the operator to make decisions regarding data throughput. If data throughput is low, the operator may choose to select a different transmission protocol or to increase the power of the radio transmitter. For example, a low Received Signal Strength Indicator (RSSI) may alert the operator to increase the transmitter power so that the receiving station may receive a clear signal. The Received Signal Strength Indicator (RSSI) and a Service Access Tone (SAT) are two indications of cellular telephone channel quality which are typically present within a known cellular telephone system. Additionally, information about the bit error rate experienced within the cellular telephone transmission channel may also be utilized by the operator to choose protocols that enhance the efficiency of data transfer.
While existing cellular telephone systems may provide channel information, such as Received Signal Strength Indicator (RSSI), Service Access Tone (SAT), bit error rates and packet counts, these important operational parameters are not generally available to data radio operators during data transmission. In order to access this information utilizing known data radio devices, the data transmission mode must be terminated and the operator must enter the command mode in order to query the status of these various parameters.
It should therefore be apparent that a need exists for a method and system whereby modem commands may be selectively processed during data transfer, resulting in the ability to poll communication channel parameters during actual data transfer.